icasefs: add test for case preservation on case insensitive filesystem "hg qpush" causes unexpected behavior, if case preservation on case insensitive filesystem is not enough. this patch adds the test using mixed-case filenames to reproduce this problem on any case insensitive filesystems.

i18n: use "encoding.lower()" to normalize string in hgweb search query some problematic encoding (e.g.: cp932) uses ASCII alphabet characters in byte sequence of multi byte characters. "str.lower()" on such byte sequence may treat distinct characters as same one, and cause unexpected log matching. this patch uses "encoding.lower()" instead of "str.lower()" to normalize strings for compare.